DyFeCo 與TbFeCo交換耦合雙層碟片在磁性質與記錄特性之比較

Abstract

光寫磁讀的記錄方式是下一代超高容量記錄中的關鍵技術。因為他結合了磁記錄和磁光記錄的優點，並且利用垂直式記錄的方式，同時克服了傳統硬碟和磁光碟片所遭遇的問題。TbFeCo是屬於非晶相的稀土-過渡金屬的合金，因具備了特殊的磁性質，已廣泛的用作磁光記錄的記錄層。近年來，由於成本的考量，使得與Tb (terbium) 同樣是稀土族的Dy (dysprosium) 越來越受到重視。本論文的主要目標是要比較TbFeCo與DyFeCo這兩個系列薄膜的磁性質與記錄特性，並且評估在作為光寫磁讀的記錄媒體方面，是否有可能以Dy來取代Tb。此外，隨著記錄密度的提高，表面入射的碟片也漸漸成為了未來的趨勢。所以，本論文在碟片的寫入測試中會以表面入射的碟片為基礎，還會探討其記錄特性和Al反射層厚度之間的關係。 我們發現單層的TbFeCo薄膜具有較高的磁化量，而且對於成分的變化較不敏感，比單層的DyFeCo薄膜較適合作為記錄層的材料。然而，光寫磁讀的記錄方式需要同時具有高矯頑場（coercivity）和高磁化量（magnetization）的記錄媒體。而單層的DyFeCo和TbFeCo因受限於材料本身，無法同時達到此兩個條件，因此，在下一個階段便針對雙層的交換耦合碟片（ECDL disk）進行分析與比較。我們發現雙層的TbFeCo disk其矯頑場會因為磁性薄膜之間的交換耦合有較大的增強，仍然是較合適的記錄層材料。另外，用動態光碟測試機做寫入的實驗，我們還可以得知DyFeCo和TbFeCo ECDL disk可以將寫入磁場（writing field）降低到200 Oe，改善了單層的磁性薄膜在寫入時需要較高寫入場的缺點。而在記錄特性和鋁（Al）反射層厚度的實驗當中，我們還發現了載波雜訊比（carrier-to-noise ratio）會隨著Al的厚度增加而增加;反之雜訊（noise level）和寫入磁場則會隨著Al的厚度增加而減小。

Hybrid recording is a key technology for the next generation ultra-high density storage. Combining the advantages of both magnetic and magneto-optical recording and utilizing the perpendicular recording media makes it possible to overcome the limitations in conventional hard disk and MO recording. TbFeCo, one of the amorphous rare earth(RE)-transition metal(TM) alloys, is the most popular commercial MO media. In recent years, Dy has attracted more and more attentions in MO recording because it costs less than Tb. The objective of this work is to compare the magnetic properties and recording characteristics between DyFeCo and TbFeCo series for hybrid recording and assess the possibility of adopting Dy instead of Tb as hybrid recording media. Besides, the writing performance of surface incident disks with various aluminum thickness was examined. We found that single layer TbFeCo possessing higher magnetization and less sensitive to the composition was more suitable recording media. However, both of these two alloys cannot satisfy the requirements of large coercivity and high magnetization simultaneously for hybrid recording. The study then moved to exchange couple dual layer (ECDL) disks, eventually the results strongly suggested that TbFeCo series was more suitable alloy due to larger coercivity enhancement. From the dynamic testing, both DyFeCo and TbFeCo ECDL disk reduce the writing field to 200Oe compared with single layer disks. On the other hand, in the writing performance v.s. Al thickness experiment, the carrier-to-noise ratio increases and the noise level and writing field decrease with the increasing Al thickness.